Nanosystems Initiative Munich NIM

München, Germany

Nanosystems Initiative Munich NIM

München, Germany
SEARCH FILTERS
Time filter
Source Type

Lee D.-J.,Ludwig Maximilians University of Munich | He D.,Ludwig Maximilians University of Munich | Kessel E.,Ludwig Maximilians University of Munich | Padari K.,University of Tartu | And 6 more authors.
Journal of Controlled Release | Year: 2016

Small interfering RNA (siRNA) promises high efficacy and excellent specificity to silence the target gene expression, which shows potential for cancer treatment. However, systemic delivery of siRNA with selectivity to the tumor site and into the cytosol of tumor cells remains a major limitation. To achieve this, we generated oligoaminoamide-based sequence-defined polycationic oligomers by solid-phase assisted synthesis, which can form polyplexes with anionic siRNA by electrostatic interaction to serve as siRNA carrier. Targeting for folate receptor (FR)-overexpressing tumors, we optimized the physicochemical properties of polyplexes by combinatorial optimization of PEGylated folate-conjugated oligomer (for FR targeting and shielding of surface charges) and 3-arm oligomer (for size modification and particle stability). For uni-directional fast coupling between the two groups of oligomers, we activated the cysteine thiol groups of one of the oligomers with 5,5′-dithio-bis(2-nitrobenzoic acid) to achieve a fast chemical linkage through disulfide formation with the free thiol groups of the other oligomer. These targeted combinatorial polyplexes (TCPs) are homogeneous spherical particles with favorable size and surface charge, which showed strong siRNA binding activity. TCPs were internalized into cells by FR-mediated endocytosis, triggered significant eGFP-luciferase marker gene silencing, and transfection with antitumoral EG5 siRNA suppressed cell proliferation in FR-expressing tumor cells. Moreover, the most promising formulation TCP1 after i.v. administration in tumor-bearing mice exhibited siRNA delivery into the tumor, resulting in EG5 gene silencing at mRNA level. Therefore, by covalent combination of two sequence-defined functional oligomers, we developed a siRNA carrier system with optimized size and surface charge for efficient tumor cell-directed gene silencing and cytotoxicity in vitro and in vivo. © 2016 Elsevier B.V.


Kriegel I.,Ludwig Maximilians University of Munich | Kriegel I.,Polytechnic of Milan | Wisnet A.,Nanosystems Initiative Munich NIM | Wisnet A.,Ludwig Maximilians University of Munich | And 9 more authors.
Journal of Materials Chemistry C | Year: 2014

Rod-shaped CdTe-Cu2-xTe nano-heterostructures with tunable dimensions of both sub-units and a type II band alignment were prepared by Cd2+/Cu+ cation exchange. The light absorption properties of the heterostructures are dominated by the excitonic and plasmonic contributions arising, respectively, from the CdTe and the Cu2-xTe sub-units. These results were confirmed over a wide range of sub-unit length fractions through optical modelling based on the discrete dipole approximation (DDA). Although assuming electronically independent sub-units, our modelling results indicate a negligible ground state interaction between the CdTe exciton and the Cu2-xTe plasmon. This lack of interaction may be due to the low spectral overlap between exciton and plasmon, but also to localization effects in the vacancy-doped sub-unit. The electronic interaction between both sub-units was evaluated with pump-probe spectroscopy by assessing the relaxation dynamics of the excitonic transition. In particular, the CdTe exciton decays faster in the presence of the Cu2-xTe sub-unit, and the decay gets faster with increasing its length. This points towards an increased probability of Auger mediated recombination due to the high carrier density in the Cu 2-xTe sub-unit. This indication is supported through length-fraction dependent band structure calculations, which indicate a significant leakage of the CdTe electron wavefunction into the Cu2-xTe sub-unit that increases along with the shortening of the CdTe sub-unit, thus enhancing the probability of Auger recombination. Therefore, for the application of type II chalcogenide-chalcogenide heterostructures based on Cu and Cd for photoenergy conversion, a shorter Cu-based sub-unit may be advantageous, and the suppression of high carrier density within this sub-unit is of high importance. This journal is © the Partner Organisations 2014.


Berkes B.B.,Eötvös Loránd University | Berkes B.B.,Karlsruhe Institute of Technology | Bandarenka A.S.,Nanosystems Initiative Munich NIM | Bandarenka A.S.,TU Munich | Inzelt G.,Eötvös Loránd University
Journal of Physical Chemistry C | Year: 2014

Electropolymerization is a promising route to design new functional surfaces. In this work, we investigate electropolymerization of indole at polycrystalline Pt electrode surfaces in acidic sulfuric media using in situ nanogravimetry, electrochemical impedance spectroscopy, and direct current (dc) measurements applied simultaneously to elucidate the physical model of the electrified interface during this process. Monitoring the electrode mass change with a quartz crystal nanobalance allows quantification of the overall electropolymerization kinetics and, together with the dc-response, provides further insight into the dynamics of the film formation. Complementary electrochemical impedance spectroscopy measurements quantify specific parameters characterizing the processes which involve the interfacial charge transfer during the film growth. Importantly for various applications, it has been also demonstrated that the growth of polyindole thin films can be controlled using just molecular oxygen dissolved in the electrolytes. © 2015 American Chemical Society.


Brenneis A.,TU Munich | Gaudreau L.,ICFO - Institute of Photonic Sciences | Seifert M.,TU Munich | Karl H.,University of Augsburg | And 6 more authors.
Nature Nanotechnology | Year: 2015

Non-radiative transfer processes are often regarded as loss channels for an optical emitter because they are inherently difficult to access experimentally. Recently, it has been shown that emitters, such as fluorophores and nitrogen-vacancy centres in diamond, can exhibit a strong non-radiative energy transfer to graphene. So far, the energy of the transferred electronic excitations has been considered to be lost within the electron bath of the graphene. Here we demonstrate that the transferred excitations can be read out by detecting corresponding currents with a picosecond time resolution. We detect electronically the spin of nitrogen-vacancy centres in diamond and control the non-radiative transfer to graphene by electron spin resonance. Our results open the avenue for incorporating nitrogen-vacancy centres into ultrafast electronic circuits and for harvesting non-radiative transfer processes electronically. © 2015 Macmillan Publishers Limited.


Erhard N.,TU Munich | Zenger S.,TU Munich | Morkotter S.,TU Munich | Rudolph D.,TU Munich | And 9 more authors.
Nano Letters | Year: 2015

We investigate the ultrafast optoelectronic properties of single Al0.3Ga0.7As/GaAs core-shell nanowires. The nanowires contain GaAs-based quantum wells. For a resonant excitation of the quantum wells, we find a picosecond photocurrent which is consistent with an ultrafast lateral expansion of the photogenerated charge carriers. This Dember-effect does not occur for an excitation of the GaAs-based core of the nanowires. Instead, the core exhibits an ultrafast displacement current and a photothermoelectric current at the metal Schottky contacts. Our results uncover the optoelectronic dynamics in semiconductor core-shell nanowires comprising quantum wells, and they demonstrate the possibility to use the low-dimensional quantum well states therein for ultrafast photoswitches and photodetectors. © 2015 American Chemical Society.


Estrada-Vargas A.,Ruhr University Bochum | Bandarenka A.,Nanosystems Initiative Munich NIM | Bandarenka A.,TU Munich | Kuznetsov V.,Ruhr University Bochum | And 2 more authors.
Analytical Chemistry | Year: 2016

Control over the properties of ultrathin films plays a crucial role in many fields of science and technology. Although nondestructive optical and electrical methods have multiple advantages for local surface characterization, their applicability is very limited if the surface is in contact with an electrolyte solution. Local electrochemical methods, e.g., scanning electrochemical microscopy (SECM), cannot be used as a robust alternative yet because their methodological aspects are not sufficiently developed with respect to these systems. The recently proposed scanning electrochemical impedance microscopy (SEIM) can efficiently elucidate many key properties of the solid/liquid interface such as charge transfer resistance or interfacial capacitance. However, many fundamental aspects related to SEIM application still remain unclear. In this work, a methodology for the interpretation of SEIM data of "charge blocking systems" has been elaborated with the help of finite element simulations in combination with experimental results. As a proof of concept, the local film thickness has been visualized using model systems at various tip-to-sample separations. Namely, anodized aluminum oxide (Al2O3, 2-20 nm) and self-assembled monolayers based on 11-mercapto-1-undecanol and 16-mercapto-1-hexadecanethiol (2.1 and 2.9 nm, respectively) were used as model systems. (Figure Presented). © 2016 American Chemical Society.


PubMed | Ruhr University Bochum and Nanosystems Initiative Munich NIM
Type: Journal Article | Journal: Analytical chemistry | Year: 2016

Control over the properties of ultrathin films plays a crucial role in many fields of science and technology. Although nondestructive optical and electrical methods have multiple advantages for local surface characterization, their applicability is very limited if the surface is in contact with an electrolyte solution. Local electrochemical methods, e.g., scanning electrochemical microscopy (SECM), cannot be used as a robust alternative yet because their methodological aspects are not sufficiently developed with respect to these systems. The recently proposed scanning electrochemical impedance microscopy (SEIM) can efficiently elucidate many key properties of the solid/liquid interface such as charge transfer resistance or interfacial capacitance. However, many fundamental aspects related to SEIM application still remain unclear. In this work, a methodology for the interpretation of SEIM data of charge blocking systems has been elaborated with the help of finite element simulations in combination with experimental results. As a proof of concept, the local film thickness has been visualized using model systems at various tip-to-sample separations. Namely, anodized aluminum oxide (Al2O3, 2-20 nm) and self-assembled monolayers based on 11-mercapto-1-undecanol and 16-mercapto-1-hexadecanethiol (2.1 and 2.9 nm, respectively) were used as model systems.


PubMed | TU Munich, Northwestern University and Nanosystems Initiative Munich NIM
Type: Journal Article | Journal: ACS nano | Year: 2015

GaAs-AlxGa1-xAs (AlGaAs) core-shell nanowires show great promise for nanoscale electronic and optoelectronic devices, but the application of these nonplanar heterostructures in devices requires improved understanding and control of nanoscale alloy composition and interfaces. Multiple researchers have observed sharp emission lines of unknown origin below the AlGaAs band edge in photoluminescence (PL) spectra of core-shell nanowires; point defects, alloy composition fluctuations, and self-assembled quantum dots have been put forward as candidate structures. Here we employ laser-assisted atom probe tomography to reveal structural and compositional features that give rise to the sharp PL emission spectra. Nanoscale ellipsoidal Ga-enriched clusters resulting from random composition fluctuations are identified in the AlGaAs shell, and their compositions, size distributions, and interface characteristics are analyzed. Simulations of exciton transition energies in ellipsoidal quantum dots are used to relate the Ga nanocluster distribution with the distribution of sharp PL emission lines. We conclude that the Ga rich clusters can act as discrete emitters provided that the major diameter is 4 nm. Smaller clusters are under-represented in the PL spectrum, and spectral lines of larger clusters are broadened, due to quantum tunneling between clusters.


Blanch A.J.,Ludwig Maximilians University of Munich | Doblinger M.,Nanosystems Initiative Munich NIM | Doblinger M.,Ludwig Maximilians University of Munich | Rodriguez-Fernandez J.,Ludwig Maximilians University of Munich
Small | Year: 2015

Branched gold nanoparticles with sharp tips are considered excellent candidates for sensing and field enhancement applications. Here, a rapid and simple synthesis strategy is presented that generates highly branched gold nanoparticles with hollow cores and a ca.100% yield through a simple one-pot seedless reaction at room temperature in the presence of Triton X-100. It is shown that multibranched hollow gold nanoparticles of tunable dimensions, branch density and branch length can be obtained by adjusting the concentrations of the reactants. Insights into the formation mechanism point toward an aggregative type of growth involving hollow core formation first, and branching thereafter. The pronounced near-infrared (NIR) plasmon band of the nanoparticles is due to the combined contribution from hollowness and branching, and can be tuned over a wide range (≈700-2000 nm). It is also demonstrated that the high environmental sensitivity of colloidal dispersions based on multibranched hollow gold nanoparticles can be boosted even further by separating the nanoparticles into fractions of given sizes and improved monodispersity by means of a glycerol density gradient. The possibility to obtain highly monodisperse multibranched hollow gold nanoparticles with predictable dimensions (50-300 nm) and branching and, therefore, tailored NIR plasmonic properties, highlights their potential for theranostic applications. Gold nanoparticles with multiple branches and hollow cores are synthesized in high yield in a simple one-pot seedless process. The plasmon resonance of the nanoparticles is tunable across the NIR, and its NIR character stems from the combined contribution of hollowness and branching. It is also shown how the high environmental sensitivity of the nanoparticles can be significantly boosted through centrifugal size sorting. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Sichert J.A.,Ludwig Maximilians University of Munich | Tong Y.,Ludwig Maximilians University of Munich | Mutz N.,Ludwig Maximilians University of Munich | Vollmer M.,Ludwig Maximilians University of Munich | And 11 more authors.
Nano Letters | Year: 2015

Organometal halide perovskites have recently emerged displaying a huge potential for not only photovoltaic, but also light emitting applications. Exploiting the optical properties of specifically tailored perovskite nanocrystals could greatly enhance the efficiency and functionality of applications based on this material. In this study, we investigate the quantum size effect in colloidal organometal halide perovskite nanoplatelets. By tuning the ratio of the organic cations used, we can control the thickness and consequently the photoluminescence emission of the platelets. Quantum mechanical calculations match well with the experimental values. We find that not only do the properties of the perovskite, but also those of the organic ligands play an important role. Stacking of nanoplatelets leads to the formation of minibands, further shifting the bandgap energies. In addition, we find a large exciton binding energy of up to several hundreds of meV for nanoplatelets thinner than three unit cells, partially counteracting the blueshift induced by quantum confinement. Understanding of the quantum size effects in perovskite nanoplatelets and the ability to tune them provide an additional method with which to manipulate the optical properties of organometal halide perovskites. © 2015 American Chemical Society.

Loading Nanosystems Initiative Munich NIM collaborators
Loading Nanosystems Initiative Munich NIM collaborators